The Queen's backed out here (8)
I believe the answer is:
republic
'here' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.
'the queen's backed out' is the wordplay.
'the queen' becomes 'er' (Elizabeth Regina).
'backed' says the letters should be written backwards.
'out' becomes 'public' (I can't justify this - if you can you should believe this answer much more).
'er' backwards is 're'.
're'+'public'='REPUBLIC'
(Other definitions for republic that I've seen before include "Political system of government by the people" , "Country in which supreme power is held by the people" , "Non-monarchical state" , "Plato's ideal state" , "Nation in which the head of state is elected" .)